1. Field of the Invention
The present invention relates to an antenna for receiving electromagnetic waves in the gigahertz range, and more particularly to an antenna and grounding surface arrangement to accommodate reception of circularly or vertically polarized electromagnetic waves.
2. Description of the Related Technology
Antennas, especially mobile antennas located in or on motor vehicles, for receiving circularly polarized electromagnetic waves emitted from satellites, or vertically polarized electromagnetic waves emitted from terrestrial transmitters, are known. A problem arising with such vehicle mounted antennas is that the direction to the one or more emitting satellites or transmitters cannot be determined beforehand. Therefore, the known antennas with small angular cones of reception suffer from reception interruptions when there are travel direction changes with respect to one or more satellites. In such circumstances there may be only emissions from one satellite that can be received, or there can be complete interruption of reception from any satellite or terrestrial transmitter.
An object of the invention is to provide an antenna that avoids the above described disadvantages, i.e. an antenna that provides almost uninterrupted reception of electromagnetic waves.
The antenna of the invention includes a resonator having an electrically nonconductive opening. The antenna resonator of the invention is located over a grounding surface to receive right- or left-circularly polarized electromagnetic waves within a conical directional pattern having an vertex angle of up to 160xc2x0. The conical directional pattern is perpendicular to the grounding surface. In part, the antenna resonator includes a resonator cup with a dielectric. Received electromagnetic waves pass through the electrically nonconductive opening into the resonator. The antenna resonator includes a dielectric and, in part, can also contain air, which can ensure especially high quality optimum reception of electromagnetic waves. Moreover, due to the configuration of the resonator with its resonator cup which holds the dielectric, it is feasible to receive circularly polarized electromagnetic waves in the gigahertz range within a conical directional pattern having a very large vertex angle, for example of up to 160xc2x0. In this way a mobile arrangement of the antenna in relation to an individual satellite, or also two or more satellites far from one another, can receive electromagnetic waves without difficulty. Based on the implemented conical directional pattern having a large vertex angle, almost interference-free and mainly uninterrupted reception of satellite signals is possible. In addition, omnidirectional reception of vertically polarized electromagnetic waves at even extremely flat angles of incidence which can be present when the signals are emitted from stationary terrestrial transmitters is possible.
For one embodiment of the invention, the dielectric has an electrically conductive coating which includes a nonconductive opening portion to the resonator for injection electromagnetic waves. The opening is for example made as a peripheral gap or slot. The dielectric itself may be for example a circuit board which is coated with an electrically conductive layer (for example, made of copper), or may be a hexaflouride (HF) substrate, such as for example TEFLON(copyright), which can be coated with an electrically conductive layer. Based on the configuration of the dielectric a large bandwidth may be received. At the same time, high reproducibility of the electrical properties can be achieved, especially in serial production of the antenna. Moreover, the dielectric with its peripheral gap nonconductive opening, and with its electrically conductive coating can be produced easily and economically. In a preferred embodiment of the invention the dielectric is held in a peripheral recess of a resonator cup. In this way the dielectric, when the antenna is installed, can be inserted or pressed into the peripheral recess so that economical production of the antenna is ensured.
In a preferred embodiment of the invention the dielectric is located parallel and above a bottom of the resonator cup. The electrically nonconductive opening of the resonator is raised over the grounding surface by a certain number of wavelengths in order to achieve the desired directional pattern. Here the dielectric is advantageously located roughly 0.05 to 0.5 wavelengths above the bottom of the resonator cup. Depending on the desired directional pattern, therefore the peripheral recess in the resonator cup can be located at a corresponding distance above the bottom of the resonator cup. This corresponding distance can be provided by there already being a peripheral recess when the resonator cup is manufactured, or the peripheral recess can be made subsequently, after production of the resonator cup.
In a preferred embodiment of the invention an electrical connection to the antenna is arranged symmetrically with respect to the resonator cup, especially with respect to the dielectric. This symmetrical arrangement of the electrical connection enables matching to the characteristic wave impedance, for example a wave impedance of 50 ohms.
In a preferred embodiment of the invention the resonator cup is made as a pressure diecasting. This has the advantage that on the one hand a pressure diecasting with a highly conductive surface can be produced, while such pressure diecasting requires only little or no reworking so that in this way production costs are reduced. In addition, such pressure in diecasting meets mechanical requirements (such as especially impacts or vibrations) in mobile use of the antenna in motor vehicles.
In a preferred embodiment of the invention, the antenna is located in a housing, and the antenna in its housing can be located on the outside skin of a motor vehicle. Alternatively or in addition (especially when there are to be several antennas in or on the motor vehicle) the antenna can also be located underneath an electrically nonconductive outside skin of the motor vehicle. It is especially advantageous here if an antenna amplifier is located within the resonator cup or within the housing of the antenna. In this way an antenna module can be produced which can be checked for its serviceability and which is supplied to the motor vehicle manufacturer for installation in new vehicles or for subsequent installation.